1. Field of the Invention
The present invention relates to a method for transferring a telephone call to a desired destination.
2. Related Background Art
The transfer of an external call has been conducted by a communication apparatus or an internal exchange apparatus with a call transfer function for transferring an incoming call from an analog channel, utilizing another analog channel.
Also the recent progress in ISDN (integrated service digital network) has enabled transfer of an external call, utilizing the supplementary service of ISDN. Such external call transfer relies on "transfer during communication" (a function for transferring a call, in communication by the user, to a third party) or "incoming call transfer" (a function for transferring an incoming call to a third party, without responding to said incoming call), which are the additional services of the ISDN. After such "transfer during communication" or "incoming call transfer" based on the additional services of the ISDN, the call between the transferring side and the ISDN is disconnected. Therefore the ISDN channel at the transferring side is not occupied, and no deterioration of information is involved.
However, after such external call transfer utilizing the additional services of the ISDN, since the call is disconnected from the transferring side as explained above, the state of the transferred call becomes utterly unclear to the transferring side.